When determining spore wall thickness ignore any ornamentation such as ridges or warts and ensure that the wall is in focus at the equatorial plane. The equatorial plane is the broadest slice if the spore were sliced into thin parallel slices perpendicular to the axis passing from the object observed to the eyepiece.

Spore wall thickness may be easier to determine in Melzer's Reagent (where spores react with this) or in coloured mounting media such as Congo Red solution.

Choose this state if: the spore wall is distinctly thickened. Often, an inner and outer wall can be discerned as darker lines, with a paler area in between. Thickened walls vary from about 1 micrometre to several micrometres thick.